WASHINGTON (AP), Mar 01 - Officials for a California gas company involved in a deadly pipeline accident last September acknowledged Tuesday that four years before the accident they rejected installing valves that could have automatically shut off or remotely controlled the flow of gas.

Pacific Gas and Electric Co. employees were questioned at a National Transportation Safety Board hearing about a company 2006 memo that said installing the valves would have ``little or no effect on increasing human safety or protecting properties.''

Gas engineer Chih-hung Lee, author of the memo, said he considered only industry studies, not government studies, in reaching his conclusions. Industry studies, he said, found that most of the damage in gas pipeline accidents occurs in the first 30 seconds after the accident.

However, when the pipeline ruptured on Sept. 9 underneath a suburban San Francisco subdivision, gas continued to feed a pillar of fire for an hour and a half before workers could manually shut off the flow. Eight people were killed, many more injured and dozens of homes destroyed.

Investigators pointed to a 1999 Transportation Department study that warned that there is a significant safety risk as long as gas was being supplied to the rupture site and operators lacked the ability to quickly close manual valves.

``Any fire would have greater intensity and would have greater potential for damaging surrounding infrastructure if it is constantly replenished with gas,'' the government study said. ``The degree of disruption in heavily populated and commercial areas would be in direct proportion to the duration of the fire.''

Coroner's reports indicate at least five of the people killed in San Bruno were trying to flee when they died.

Keith Slibasager, PG&E's manager of gas system operations, said it took control room employees about 15 minutes following the explosion to figure out what had happened and would have taken about another 15 minutes to shut off the gas using automatic or remotely controlled valves. That's an hour less than it took in San Bruno.

Instead, about 12 minutes after the explosion, PG&E's dispatch center sent an off-duty employee to investigate the reported explosion, but he wasn't qualified to operate the manual valves needed to shut off gas feeding a huge fire that consumed homes, the safety board investigator Ravi Chhatre said.

It took 30 minutes after the rupture for the company to dispatch a crew capable of isolating the pipeline and 90 minutes for them to crank the valves shut, stopping all gas, he said.

PG&E officials acknowledged that after Lee's memo they made no effort to further explore the valves. They said that since the disaster, the company has begun a pilot project to install a dozen of the valves this year and study their effectiveness.

PG&E ``is committed to expanding the use of these valves where appropriate and is working with industry experts to study the best use of those valves,'' the company said in a statement distributed during the hearing.

But Slibasager said there are potential safety drawbacks to the valves. When closed, they could cause widespread gas outages in the region that would put out pilot lights in homes and other buildings, he said. That poses the risk that when gas is turned back on, it could build up in buildings in which pilot lights are not relit right away, he said.

Lee's memo was at odds with a 1996 report by another PG&E employee. The employee, Bob Becken, was assigned to study the effectiveness of remote-control valves suggested that more needed to be installed in the system.

In a memo released by the NTSB, Becken said he had ``no concerns'' about installing remote-control valves. ``There are existing places within PG&E's gas transmission system where we should consider installing them in the future,'' he wrote.

The safety board has been recommending the devices to industry and regulators for decades for gas distribution lines, which are larger than the transmission line that ruptured in San Bruno.

The utility has said it installed approximately 60 remote-control valves over the past several decades across its 6,700 miles of transmission lines. That's about one for every 111 miles of pipeline on average.

The hearing also focused on PG&E's erroneous listing of the San Bruno pipeline as a ``seamless'' line, considered stronger than pipelines that have been welded together. It was discovered after the accident that welded pipe was used in San Bruno and that the welds were inferior.

PG&E said in other documents released by NTSB that its personnel improperly relied on records from the utility's accounting department to determine the type of pipeline, rather than engineering documents that showed the correct type.

There were numerous indications coming into PG&E's control room in the hour leading up to the San Bruno explosion that there was a problem with the utility's transmission system. A power interruption at a PG&E terminal 39 miles from San Bruno in Milpitas had caused gas pressure levels to spike in some pipelines in the area.

By 6:02 p.m. - just nine minutes before the blast - a gas control operator identified in control room transcripts only as ``Larry'' reported those pressure problems had spread far beyond Milpitas.

``We've got a major, major problem at Milpitas and we've overpressured the whole peninsula,'' the gas control operator said.

The explosion itself seemingly went unnoticed by those in the control room until a dispatcher called at 6:27 to say he'd received reports of a three-story-tall flame towering over San Bruno.

``In San Bruno?'' the gas control operator replied. ``We have not received any calls yet.''

A minute later the operator said he was ``watching the (gas) pressure just plummet like a rock'' to 56 pounds per square inch from its peak pressure of 396 pounds per square inch.

The pipe that ruptured was allowed to have maximum pressure of up to 400 pounds per square inch. But that assumed incorrectly that the pipe was seamless.

The 396 pounds per square inch in the transcripts is also 10 pounds per square inch higher than previously reported by NTSB and PG&E. Company officials said again at the hearing that the pressure in the ruptured pipe didn't exceed 386 pounds.